1. Field of the Invention
The present invention relates to an electric motor drive system, an electric four-wheel drive vehicle, and a hybrid vehicle, and particularly to an electric motor control system for controlling a generator and electric motor, and an electric four-wheel drive vehicle and hybrid vehicle including such an electric motor control system.
2. Description of the Related Art
As a control device for a hybrid vehicle, a series hybrid vehicle is known as disclosed in JP-A-11-332007, for example. The aforementioned series hybrid vehicle has a configuration in which an output shaft of an engine is mechanically separated from a vehicle driving shaft. With such a configuration, the electrical energy generated by a generator driven by the engine is supplied to a driving electric motor, and the vehicle is driven using the output torque.
Also, a hybrid vehicle is known, which has a battery for temporarily storing generated electrical power and regenerative electrical power, as disclosed in JP-A-11-332007. With such an arrangement, at the time of controlling the vehicle speed or braking the vehicle, the driving generator is used as a regenerative brake, and the regenerative energy generated in this stage is stored in the battery, thereby enabling the energy generated in the reduction of the vehicle speed to be effectively used. On the other hand, it is known that in a case where the battery for absorbing the regenerative energy is almost fully charged, the regenerative electrical power continuously generated by the driving generator leads to overcharge of the battery. In order to prevent such a situation, a technique is known that in a case of the battery being almost fully charged, the generator is operated in the power-running state with the rotational resistance of the engine as a load so as to consume the regenerative current.
Also, another control method is known for consuming excess regenerative energy, which can be applied irrespective of whether or not the engine is connected to the generator, as disclosed in JP-A-2003-134602. Specifically, JP-A-2003-134602 discloses a hybrid vehicle having a configuration in which in a case that the battery cannot absorb the regenerative energy, the generator is controlled so as to operate with loss of energy, thereby consuming the excess regenerative energy.